This invention relates to an improved apparatus for separating a component from a fluid stream. In one embodiment, the fluid may be a gas having solid and/or liquid particles and/or a second gas suspended, mixed, or entrained therein and the separator is used to separate the particles and/or the second gas from the gas stream. In an alternate embodiment, the fluid may be a liquid which has solid particles, and/or a second liquid and/or a gas suspended, mixed, or entrained therein and the separator is used to remove the solid particles and/or the second liquid and/or the gas from the liquid stream. The improved separator may be used in various applications including vacuum cleaners, liquid/liquid separation, smoke stack scrubbers, pollution control devices, mist separators, an air inlet for a turbo machinery and as pre-treatment equipment in advance of a pump for a fluid (either a liquid, a gas or a mixture thereof) and other applications where it may be desirable to remove particulate or other material separable from a fluid in a cyclone separator.
Cyclone separators are devices that utilize centrifugal forces and low pressure caused by spinning motion to separate materials of differing density, size and shape. FIG. 1 illustrates the operating principles in a typical cyclone separator (designated by reference numeral 10 in FIG. 1) which is in current use. The following is a description of the operating principles of cyclone separator 10 in terms of its application to removing entrained particles from a gas stream, such as may be used in a vacuum cleaner.
Cyclone separator 10 has an inlet pipe 12 and a main body comprising upper cylindrical portion 14 and lower frusto-conical portion 16. The particle laden gas stream is injected through inlet pipe 12 which is positioned tangentially to upper cylindrical portion 14. The shape of upper cylindrical portion 14. and frusto-conical portion 16 induces the gas stream to spin creating a vortex. Larger or more dense particles are forced outwards to the walls of cyclone separator 10 where the drag of the spinning air as well as the force of gravity causes them to fall down the walls into an outlet or collector 18. The lighter or less dense particles, as well as the gas medium itself, reverses course at approximately collector G and pass outwardly through the low pressure centre of separator 10 and exit separator 10 via gas outlet 20 which is positioned in the upper portion of upper cylindrical portion 14.
The separation process in cyclones generally requires a steady flow free of fluctuations or short term variations in the flow rate. The inlet and outlets of cyclone separators are typically operated open to the atmosphere so that there is no pressure difference between the two. If one of the outlets must be operated at a back pressure, both outlets would typically be kept at the same pressure.
When a cyclone separator is designed, the principal factors which are typically considered are the efficiency of the cyclone separator in removing particles of different diameters and the pressure drop associated with the cyclone operation. The principle geometric factors which are used in designing a cyclone separator are the inlet height (A); the inlet width (B); the gas outlet diameter (C); the outlet duct length (D); the cone height (Lc); the dirt outlet diameter (G); and, the cylinder height (L)
The value d50 represents the smallest diameter particle of which 50 percent is removed by the cyclone. Current cyclones have a limitation that the geometry controls the particle removal efficiency for a given particle diameter. The dimensions which may be varied to alter the d50 value are features (A)-(D), (G), (L) and (Lc) which are listed above.
Typically, there are four ways to increase the small particle removal efficiency of a cyclone. These are (1) reducing the cyclone diameter; (2) reducing the outlet diameter; (3) reducing the cone angle; and (4) increasing the body length. If it is acceptable to increase the pressure drop, then an increase in the pressure drop will (1) increase the particle capture efficiency; (2) increase the capacity and (3) decrease the underflow to throughput ratio.
In terms of importance, it appears that the most important parameter is the cyclone diameter. A smaller cyclone diameter implies a smaller d50 value by virtue of the higher cyclone speeds and the higher centrifugal forces which may be achieved. For two cyclones of the same diameter, the next most important design parameter appears to be L/d, namely the length of the cylindrical section 14 divided by the diameter of the cyclone and Lc/d, the length of the conical section 16 divided by the width of the cone. Varying L/d and Lc/d will affect the d50 performance of the separation process in the cyclone.
Typically, the particles which are suspended or entrained in a gas stream are not homogeneous in their particle size distribution. The fact that particle sizes take on a spectrum of values often necessitates that a plurality of cyclonic separators be used in a series. For example, the first cyclonic separator in a series may have a large d50 specification followed by one with a smaller d50 specification. The prior art does not disclose any method by which a single cyclone may be tuned over the range of possible d50 values.
An example of the current limitation in cyclonic separator design is that which has been recently applied to vacuum cleaner designs. In U.S. Pat. Nos. 4,373,228; 4,571,772; 4,573,236; 4,593,429; 4,643,748; 4,826,515; 4,853,008; 4,853,011; 5,062,870; 5,078,761; 5,090,976; 5,145,499; 5,160,356; 5,255,411; 5,358,290; 5,558,697; and RE 32,257, a novel approach to vacuum cleaner design is taught in which sequential cyclones are utilized as the filtration medium for a vacuum cleaner. Pursuant to the teaching of these patents, the first sequential cyclone is designed to be of a lower efficiency to remove only the larger particles which are entrained in an air stream. The smaller particles remain entrained in the gas stream and are transported to the second sequential cyclone which is frusto-conical in shape. The second sequential cyclone is designed to remove the smaller particles which are entrained in the air stream. If larger particles are carried over into the second cyclone separator, then they will typically not be removed by the cyclone separator but exit the frusto-conical cyclone with the gas stream.
Accordingly, the use of a plurality of cyclone separators in a series is documented in the art. It is also known how to design a series of separators to remove entrained or suspended material from a fluid stream. Such an approach has two problems. First, it requires a plurality of separators. This requires additional space to house all of the separators and, secondly additional material costs in producing each of the separators. The second problem is that if any of the larger material is not removed prior to the fluid stream entering the next cyclone separator, the subsequent cyclone separator typically will allow such material to pass therethrough as it is only designed to remove smaller particles from the fluid stream.
In accordance with one embodiment of the instant invention, there is provided a non-frusto-conical cyclone separator comprising a longitudinally extending body having a wall, the wall having an inner surface and defining an internal cavity within which a fluid rotates when the separator is in use, at least a portion of the inner surface of the wall configured to continuously impart changes in the rate of acceleration to the fluid as it rotates within the cavity.
In accordance with another embodiment of the present invention, there is provided a non-frusto-conical cyclone separator comprising a longitudinally extending body having a longitudinally extending axis and a wall, the wall having an inner surface and defining an internal cavity within which a fluid rotates when the separator is in use, at least a portion of the inner surface of the wall is defined by a plurality of straight lines which approximate a continuous n-differentiable curve swept 360 degrees around the axis wherein nxe2x89xa72 and the second derivative is not zero everywhere.
In accordance with another embodiment of the present invention, there is provided a non-frusto-conical cyclone separator comprising a longitudinally extending body having a longitudinally extending axis and a wall, the wall having an inner surface and defining an internal cavity within which a fluid rotates when the separator is in use, at least a portion of the inner surface of the wall defined by a continuous n-differentiable curve swept 360 degrees around the axis wherein nxe2x89xa72 and the second derivative is not zero everywhere.
Preferably, nxe2x89xa61,000, more preferably nxe2x89xa6100 and most preferably nxe2x89xa610. The second derivative may be zero at a finite number of points and, preferably the second derivative is zero at from 2 to 100 points, more preferably 2 to 30 points and most preferably 2 to 10 points.
In one embodiment, the inner surface of the separator is continuous in the longitudinal direction.
In another embodiment, the inner surface of the wall is defined by a plurality of straight lines and preferably by 3 or more straight lines.
In another embodiment, the fluid is directed to rotate around the inner wall when the fluid enters the separator.
The fluid which is introduced into the cyclone may comprise a gas which has a material selected from the group consisting of solid particles, a liquid, a second gas and a mixture thereof contained therein and a portion of the material is removed from the gas as the gas passes through the separator.
The fluid which is introduced into the cyclone may comprise a liquid which has a material selected from the group consisting of solid particles, a second liquid, a gas and a mixture thereof contained therein and a portion of the material is removed from the liquid as the liquid passes through the separator.
The fluid which is introduced into the cyclone may comprise at least two fluids having different densities and the inner wall includes at least a portion which is configured to decrease the rate of acceleration (i.e. increase the rate of deceleration) of the fluid as it passes through that portion of the separator.
In another embodiment, the separator comprises a dirt filter for a vacuum cleaner.
The separator may have a collecting chamber in which the separated material is collected. Alternately, the separator may have a separated material outlet which is in flow communication with a collecting chamber in which the separated material is collected.
By designing a cyclone separator according to the instant invention, the parameters L/d and Lc/d may vary continuously and differentiably along the length of the cyclone axis. Thus, a cyclone may be designed which will have a good separation efficiency over a wider range of particle sizes than has heretofore been known. Accordingly, one advantage of the present invention is that a smaller number of cyclones may be employed in a particular application than have been used in the past. It will be appreciated by those skilled in the art that where, heretofore, two or more cyclones might have been required for a particular application, that only one cyclone may be required. Further, whereas in the past three to four cyclones may have been required, by using the separator of the instant intention, only two cyclones may be required. Thus, in one embodiment of the instant invention, the cyclone separator may be designed for a vacuum cleaner and may in fact comprise only a single cyclone as opposed to a multi-stage cyclone as is known in the art.